Mobility Management Entity (MME) and User Plane Entity (UPE) in an enhanced radio communication system can be combined in a same entity, where a plurality of MMEs/UPEs are connected to a plurality of ENBs and one ENB is connected to an adjacent ENB. In a communication system, MME and UPE may be two separate entities. Here, a system structure is shown in FIG. 1. More than one MMEs are connected to ENBs through S1 interface, a plurality of UPEs are connected to many ENB through S1 interface, and one ENB is connected to the adjacent ENB through X2 interface. With reference to FIG. 1, a radio communication system contains a communication trunk network 100, a group of enhanced base stations E-Node B 104 and 105, and they jointly provide services within the route area TA. Radio communication system could be, but not limited to FDMA based communication system, TDMA based communication system or CDMA based communication system. Communication trunk network 109 contains MME (mobility management entity) 103 and UPE (user plane entity) 102. Each enhanced base station 104 and 105 provides services for all communication cell 106 and 107 in a whole route area. MME103, UPE102 and E-Node B 105, complying with a practically executable standard, provide radio communication services for cell phones 108 working within the communication cell (MS), UPE102 and Anchor101 are connected, to receive the data sent by the external network from Anchor. The system components mentioned above are expected to be purchased commercially.
To make efficient use of air interface resources, some service is provided to the users in form of Multimedia Broadcast and Multicast Service (MBMS service). Each MBMS service provides services within its own service area. For each cell in the serving area, a dedicated control MCCH is adopted to transmit MBMS signaling.
In an enhanced radio communication system, some differences exist between an MBMS transmission mode and 3G. MBMS service may be transmitted in a single-carrier cell. If the same single-carrier is adopted for the transmission of MBMS service in adjacent cell and the synchronization is applied here, then the signal received by the user is superposition of the two signals. If the same MBMS service is transmitted with the same carrier but in non-synchronous mode in adjacent cells, then signals from adjacent cells cause interferences to the user and therefore MBMS receiving quality for user is affected. Thus, a continuous area is defined for an enhanced radio communication system. Within this area, all enhanced base stations share one carrier to synchronously transmit signals so as to improve the MBMS receiving quality of the user. This continuous area is called an SFN area.
Single Frequency Network (SFN) area includes cells with continuous geographical areas, these cells use the same radio resources to synchronize the transmission of a particular MBMS service. SFN area is an only service area that belongs to MBMS. One SFN area contains only the cell that is transmitting data.
MBMS service area is a specific area for MBMS Session data transmission. Multi-cell MBMS synchronization area is a group of cells, which cover a continuous area and allocate the same frequency band to MBMS service. The group of cells are able and possible to transmit MBMS data through SFN model. Multi-cell MBMS synchronization does not rely on MBMS service area, and a multi-cell MBMS synchronization area can support one or more SFN areas. For a geographical area, a designated frequency band defines only one multi-cell MBMS synchronization area. If many a multi-cell MBMS synchronization area is defined for the same geographic area, these multi-cell MBMS synchronization areas will be allocated to different frequency bands.
A multi-cell MBMS synchronization area can contain a plurality of SFN areas. To reduce interference, the adjacent SFNs must not use the same frequency.
Research shows all the enhanced base station synchronization transmitting MBMS data will bring about significant improvement in performance. There are different technologies to achieve data synchronization transmission between enhanced base stations. One is the synchronization method by the network, where the transmission network achieves synchronization with a clock, using IEEE1588 protocol. This protocol can coordinate a series of clocks at the enhanced base station, and the synchronization occurs among them, with precision being at least several microseconds. One method is through a public satellite signal, for example GPS, to transmit the synchronization signal to the enhanced base station. Another method is synchronization of air interface signal assisted by UE, and a great deal of air resources will be wasted by this method. And the detailed approach is not determined at all. Whichever approach is applied here, it aims at that the signal from the enhanced base station is synchronous so as to gain the best performance.
The MBMS data is received from the enhanced base station synchronistically, thus not only synchronization of the enhanced base station, but also the same data packets sent by the enhanced base station are desired. Therefore UE can jointly receive the signals sent by different enhanced base stations. To ensure that the data packets sent by the enhanced base station are the same, it is necessary that the enhanced base stations have the same data processing link, so that a centralized control node is needed to configure a data processing link with the enhanced base station. For example, the same RLC/MAC protocol parameter to the enhanced base station is configured. Hereinafter, a physical entity where a control module is located is called as MCE, and MCE will set the same RLC/MAC configuration for the enhanced base station within the SFN scope.
FIG. 2 shows a structure of EMBMS where MCE is a new node. MCE not only configures the SFN area but also schedules MBMS.
Cells under the coverage of SFN may be divided into three types with one is called as a transmission and announcement cell, one is called as an only transmission cell, and the rest are called as reserved cells. In the transmission and announcement cell, both control channel and data channel for eMBMS are transmitted. In the only transmission cell, only data is transmitted. And in the reserved cell, neither control channel nor data is transmitted. Resources for SFN transmission may be allocated to other services. Within the SFN coverage, a multi-cell point-to-multipoint (MC-PTM) mode, i.e., an SFN transmission mode, is adopted to transmit eMBMS data.
The cells that do not belong to the SFN coverage are common cells. And in a common cell, the single-cell point-to-multipoint (SC-PTM) transmission mode is applied.
When a user moves from a cell with the MC-PTM transmission mode into a cell with the SC-PTM transmission mode, if the user is in idle state, it is necessary to re-select a cell. And if it is a first user, it is necessary for ENB to establish a data connection with a core network. During this process, loss of data happens.
It is necessary to consider how to maintain continuous data receiving when a user moves from MC-PTM cell to either a reserved cell or an only transmission cell.